From: Sasha Levin <sashal@kernel.org>
To: stable@vger.kernel.org
Cc: Sean Christopherson <seanjc@google.com>,
	Stefan Teodorescu <fane@google.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Sasha Levin <sashal@kernel.org>
Subject: [PATCH 6.6.y] KVM: SEV: Do cache maintenance on the source VM during intra-host migration
Date: Wed, 30 Sep 2026 08:45:42 -0400
Message-ID: <20260930124542.1671035-1-sashal@kernel.org>
In-Reply-To: <2026092918-providing-domelike-5f91@gregkh>
References: <2026092918-providing-domelike-5f91@gregkh>
Precedence: bulk
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit

From: Sean Christopherson <seanjc@google.com>

[ Upstream commit 93de2a6a4b91b72607136dd656edf03fb399d27f ]

Manually perform cache maintenance on the source VM during intra-host
migration to ensure no stale data is left in CPU caches after the VM is
destroyed.  Because the source VM is "converted" to a non-SEV VM, KVM's
memory reclaim flows won't trigger cache maintenance, e.g. when all guest
memory is reclaimed in response to detaching from the mmu_notifier.

Note, relying on the destination VM to do cache maintenance isn't an option
as KVM doesn't require identical guest memory configurations, i.e. the
source VM may have access to memory that the destination VM does not.
Enforcing equivalent memory configurations is infeasible, as it would
require a *deep* comparison of memslots, e.g. to verify that not only are
the memslot identical, but what the memslots point at is also identical.

Fixes: b56639318bb2 ("KVM: SEV: Add support for SEV intra host migration")
Cc: stable@vger.kernel.org
Reported-by: Stefan Teodorescu <fane@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-ID: <20260923163721.1584779-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
[ Replaced unavailable sev_writeback_caches(src_kvm) with wbinvd_on_all_cpus(). ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 arch/x86/kvm/svm/sev.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 0ba286bd50c27..2bc25a89f36b3 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -1723,6 +1723,12 @@ static void sev_migrate_from(struct kvm *dst_kvm, struct kvm *src_kvm)
 	src->pages_locked = 0;
 	src->es_active = false;
 
+	/*
+	 * Do cache maintenance on the source VM as it is no longer an SEV VM,
+	 * i.e. memory reclaim flows won't trigger cache maintenance on the VM.
+	 */
+	wbinvd_on_all_cpus();
+
 	list_cut_before(&dst->regions_list, &src->regions_list, &src->regions_list);
 
 	mutex_lock(&sev_mirror_lock);
-- 
2.53.0